Gelatin-anion soap complex dispersion in polyvinyl alcohol photographic emulsions



nitcri uni bice Adolf Eduard Oberth, .lameshurg, and Comer DrakeShacitiett, Roselle, N.J., assignors to E. i. du Pont de Nemonrs andCompany, Wilmington, DeL, a corporation of Delaware No Drawing. FiledApr. 1, 1959, Ser. No. 803,356

11 Ciaims. (Cl. 96-114) This invention relates to photographic emulsionsand more particularly, it relates to radiation sensitive silver halideemulsions comprising silver halide dispersed in a gelatin-anion soapcomplex, said complex being dispersed in a synthetic polymer binder.Still more particularly this invention relates to processes for makingthese photographic emulsions.

Gelatin has been used for many years as a protective colloid forlight-sensitive silver halides because it has many desirablecharacteristics for this purpose. It has the ability to keep the silverhalide grains finely dispersed and inherently has the ability ofimparting non-optical sensitization to the grains. Gelatino-silverhalide emulsion layers also have good permeability to processingsolutions.

However, gelatin has many features which are troublesome in themanufacture of photographic emulsions and the coated emulsion layers.Being a natural product it is subject to deterioration bymicro-organisms. It also requires extensive testing from batch to batchbecause of non-uniformity. Gelatin layers are also very sensitive tochanges in atmospheric conditions, especially humidity and temperaturechanges. This sensitivity to variations in humidity and temperaturewhich manifests itself in one aspect by dimensional instability of thecoated layer is also one of the greatest drawbacks to the use of gelatinin modern emulsions which are utilized for cine-positive films. Suchfilms are often subjected to the heat of highintensity arc lampprojectors which are commonly in use in out-door theaters. It has beenthe custom in conventional emulsion manufacture to set the gelatinemulsion, after the silver halide grains have been formed therein, bycooling to cause gelation and then noodling the emulsion and washing thenoodles to remove the unwanted excess soluble salts. Under suchconditions, it is impractical for the gelatin concentration in theaqueous solution to exceed 8 to 15%. This limitation is quitetroublesome to the emulsion maker for obvious reasons. The necessity forusing very dilute systems also presents con siderable difiiculty incoating and drying and requires very elaborate and costly equipment forthis purpose.

More recently, the technique of removing unwanted soluble salts has beenaccomplished by coagulation washing. This is a method whereby certainchemicals are added to a gelatin silver halide dispersion containing asmall ratio of gelatin to silver halide whereby chemical complexes areformed with the gelatin which are sensitive to pH changes. By loweringthe pH the gelatin complex containing the silver halide grainscoagulates and settles out of the liquid medium and the supernatantliquid containing the soluble salts is decanted. The coagulum may bewashed as many times as is necessary with water and then redispersed inan aqueous medium by raising the pH and in turn adding the redispersedcoagulum to an aqueous solution of gelatin.

Emulsion makers for years have attempted to find a synthetic materialwhich would be suitable as a colloid carrier and dispersing agent forsilver halide grains and which would overcome the deficiencies ofgelatin. Such emulsions must possess the sensitometric characteristicsand permeability to the usual photographic processing solutionscomparable to emulsions comprising gelatin as the sole binder. Polyvinylalcohol and its various chemical analogues have been the subject ofresearch for decades in an attempt to use them as the sole or partialreplacement of gelatin as the colloid binder in photographic emulsions.Polyvinyl alcohol as a direct and complete substitute for gelatin hassome practical advantages. Polyvinyl alcohol for example has highermechanical strength and durability. Being a synthetic product it may beproduced with more uniform properties from batch to batch than in thecase of gelatin which is extracted from animal products from differentgeographical locations. Attempts have been made to mix gelatin andpolyvinyl alcohol in an amount of 120% of gelatin based on the weight ofpolyvinyl alcohol in an effort to obtain the advantages of each colloidand to minimize the deficiencies of each. Very little in the way ofpractical results has been obtained in this manner. This is mainlybecause gelatin of the quality and molecular Weight required forphotographic use is incompatible with polyvinyl alcohol having amolecular weight of sufficient magnitude to function adequately as acolloid binder. Other attempts to solve the problem have been to formchemical derivatives of gelatin by reacting it with, for example, asulfonyl chloride. Such derivatives with the silver halide grainsdispersed therein may be coagulated in an aqueous medium and washed bylowering the pH as described above with the gelatin complexes. Suchderivatives may be redispersed by raising the pH to above 6.0 and mixingan aqueous solution of the material with an aqueous solution ofpolyvinyl alcohol as the main binder. However, the reactions involvingthe formation of such derivatives are usually quite rigorous and tend toreduce the beneficial dispersing characteristics of gelatin for silverhalide grains and for this and other reasons the method of using gelatinderivatives has not been found to be practicable.

An object of this invention is to provide photographic emulsions and amethod for their preparation which are very dimensionally stable andhave high resistance to deterioration under conditions of exposure tointense heat of high intensity are light projectors.

Another object is to provide photographic emulsions and a method fortheir preparation wherein the principal colloid carried is polyvinylalcohol.

A further object is to provide photographic emulsions and a method fortheir preparation which are compatible with water soluble polyvinylalcohol solutions without the use of organic solvents in the system.Other objects will appear hereinafter.

These and other objects are accomplished by the present invention whichis a method of preparing a photographic emulsion which comprisesdispersing silver halide in an aqueous gelatin solution, adding theretoan anion soap thereby forming a gelatin-anion soap complex containingdispersed silver halide grains and dispersing the said complex in awater soluble polyvinyl alcohol binder in aqueous solution.

It has now been found that high quality photographic emulsions can bemade using a watersoluble polyvinyl alcohol polymer containing a largenumber of intralinear -CH CHOH groups as the colloid carrier bydispersing silver halides in a small quantity of aqueous gelatin by thedouble decomposition of a soluble silver salt and a soluble halide ormixture as is well known in the art. After ripening the precipitatedsilver halide grains in the usual manner, a small quantity of an anionsoap is then added to form a gelatin-anion soap complex in the mannertaught in Waller et al., U.S. 2,489,341. The complex thus formed may beprecipitated and coagulationwashed by the methods taught by Waller etal., to remove the unwanted soluble salts. After Washing, the sediclmented complexes containing the originally suspended silver halide areredispersed in an aqueous solution of a water-soluble polyvinyl alcoholbinder. The pH is adjusted by suitable means to approximately 7.0.Suitable sensitizers may then be added, and the emulsion digested in theusual manner, since such emulsions readily respond to chemicalsensitization. After digestion, final adjuvants such as antifoggant,hardeners, etc. are added and the emulsion is coated on a suitablesupport.

Polyvinyl alcohols of low, medium or high viscosity may be used. Suchcompounds are usually made by hydrolyzing polyvinyl acetate, and toobtain the required water solubility, it is necessary that at least 80%of the ester groups be hydrolyzed. Many advantages reside in preparing asilver halide emulsion in the above manner. Gelatin-anion soap complexeshaving silver halide grains dispersed therein are completel compatiblewith water soluble polyvinyl alcohol in aqueous solutions and provideemulsion layers of good clarity. Such emulsions are readily adapted tothe various manipulations carried out in the emulsion making art. Suchemulsions are easily hardened by the water-soluble titanyl complexesformed by reacting a tetraalkyl titanate with an a-hydroxy carboxylicacid. Such compounds are disclosed and claimed in Shacklett US. Patent2,870,181, January 20, 1959.

Anion soaps which are suitable for use as complexing agents include alarge variety of Water-soluble compounds which are surface-activecompounds in which the reduction in surface tension resultant on theiraddition to water is due to the anion; these are described in detail inWaller et al., US. 2,489,341. Sodium dodecyl sulfate is one member ofthe class which has been found to be particularly suitable. It readilyforms complexes with gelatin and is commercially available at relativelylow cost. In general, the quantity of the anion soap required to effecta satisfactory gelatin-anion soap complex depends on many factors sincethe exact nature of the reaction between the anion soap and the gelatinis not clear. Some of the factors are gelatin concentrations, pH valueof the solution and the nature of the anion soap itself. It is notpossible, therefore, to define exactly the best conditions for all setsof circumstances, but the optimum conditions for any particular case canreadily be ascertained by trial, usually from .75 to 1.25 parts byweight of anion soap per part of gelatin is used.

As a general procedure one may precipitate the silver halides to form asilver iodobromide in a 0.40 to 0.60% aqueous gelatin solution in anamount of from 7 to 20 grams of gelatin to one mol of silver halide. Theemulsion is ripened at from 45 to 50 C. for from to 40 minutes. Anaqueous anion-soap solution (e.g. containing 5% by weight of said anionsoap based on the weight of the water) is then added to provideapproximately an amount of anion soap equivalent to the amount ofgelatin present although this may be varied over a wide range, e.g. 75%to 125% by weight per unit weight of gelatin. Ripening may be continuedfrom 1 to 5 minutes longer depending upon the photographiccharacteristics desired in the emulsion, but can be omitted in somecases. An acid, which is innocuous to the emulsion, e.g. acetic acid, isadded to lower the pH to about 5. The amount of acid required will ofcourse vary depending on the pH of the emulsion since at this point itcontains a substan tial quantity of ammonia or electrolyte in the formof soluble salts resulting from the silver halide precipitation. Theaddition of acid brings about the coagulation of the gelatin-anion soapcomplex. The emulsion is then cooled to about to C. and the coagulumallowed to settle. The supernatant liquid is then removed by decantationor siphoning and the coagulum is washed with a 1 to 2% solution ofsodium chloride which may contain a small quantity of acid (eg. aceticacid). Within practical limits, the amount of washing solution is notcritical nor is the number of times that the coagulum is washed. It isonly necessary to wash the coagulated emulsion sufficiently to removethe unwanted soluble salts. To the coagulum there is added one liter ofdistilled water and the mixture is stirred at 43 C. for five minutes. Atthis point, deionized polyvinyl alcohol in the form of a 3.5 to 5%solution equivalent to 70 to 200 grams per mol of silver salt, is added,the pH is raised to 7.5 with sodium hydroxide, and the emulsion isstirred for 5 to 20 minutes to disperse the coagulum. The temperature israised to from 49 to 60 C., sulfur and metal sensitizers are added andthe emulsion is digested for 20 to 60 minutes. The emulsion is thencooled to about 40 to 45 C., the usual coating aids, antifoggants, etc.are added, the pH adjusted to from 8 to 10 with a suitable amine oralkali metal hydroxide, and the emulsion is coated on a suitable supportin an amount to give a coating weight of 50-150 mg. of silver halide persquare decimeter.

The emulsions may also be made by precipitating the silver halides in anaqueous gelatin solution and ripening as described above and thenwashing by coagulating the gelatin dispersion with a Water soluble, acidsoluble organic polymer as described in Moede, US. 2,772,165, i.e. thewater soluble, acid soluble partial acetal of polyvinyl alcohol and thesodium salt of o-sulfobenzaldehyde described in McQueen, US. 2,462,527and Umberger and Grumbine, US. 2,609,290. The pH is adjusted to belowthe isoelectric point of the gelatin, preferably below 4.5 and a pHbetween 2 and 3 is particularly preferred. The coagulum is thenredispersed by a readjustment of the pH to above 6, preferably between 6and 7, and the anion soap is then added as described above to form thegelatinanion soap complex. The resulting dispersion is mixed with thedeionized polyvinyl alcohol solution.

The photographic emulsions of the invention in general contain 70 to 200grams of polyvinyl alcohol or other vinyl alcohol polymer and 7 to 20grams of gelatin per mole of silver halide.

The invention will now be further illustrated by, but is not intended tobe limited to, the following examples. The emulsions are prepared andmaintained under conditions such that actinic light will not expose thesilver halide grains.

Example I A cine positive silver iodobromide emulsion containing 30grams of gelatin and approximately 2% silver iodide and 98% silverbromide based on the total weight of silver halides was made byprecipitating the silver halides in a 0.59% aqueous gelatin solution inan amount to give a ratio of gelatin to silver halide of about 1:9. Theemulsion was ripened at about 49 C. for about 17 minutes. At the end ofthis time, an aqueous solution of sodium dodecyl sulfate was added whilemaintaining the temperature at 49 C. in an amount to give a ratio ofgelatin to sodium dodecyl sulfate of 1:125. The emulsion was stirred toobtain a good mixture and then enough acetic acid (about ml.) was addedto lower the pH to about 4.5. The emulsion was cooled 15 C. and thecoagulum carrying the suspended silver iodobromide grains and formed bythe addition of sodium dodecyl sulfate and acetic acid was allowed tosettle for six minutes. The supernatant liquid was carefully decantedfrom the coagulum which was washed with about 5 liters of a 2% sodiumchloride solution under agitation for about 3 minutes. The supernatantliquid was then removed by decantation. Distilled water was added tobring the total weight up to 1000 grams and then 3000 grams of 3%%deionized high molecular weight polyvinyl alcohol (98100% hydrolysisgrade) was added to the mixture. The pH was adjusted to 7.0 with sodiumhydroxide and the coagulum was redispersed by stirring for 10 minutes.The temperature was raised to 60 C. and sensitizers were added. Theemulsion was digested for 50 minutes at 60 C. The emulsion was cooled to43 C. and final additions were made which included an antifoggant and200 ml. of a 3% aqueous solution of titanium lactate. The pH was ad-Grams Methyl-p-aminophenol hydrosulfate 3.0 Hydroquinone 9.0 Sodiumsulfite (anhydrous) 50.0 Potassium carbonate 50.0 Potassium bromide 4.5Water to make 1 liter.

Following development, the films were fixed, washed and dried in theconventional manner. The results of the sensitometric tests in terms ofrelative speed and gamma are shown in the following table.

Relative Speed Emulsion Gamma Fog Gelatin (Control) 12 2 Polyvinylalcohol emulsion 25 3.

men

can:

In referring to an all-gelatin emulsion made in a conventional manner wemean dispersing the silver halides in gelatin, coagulation-washing andthen redispersing by warming in an aqueous gelatin solution. Thepolyvinyl alcohol emulsion as compared with the control had very highresistance to dimensional change, blistering, and deterioration underthe influence of high intensity are light projection.

Example 11 A cine positive silver iodobromide emulsion was made in themanner described in Example I except that the silver halides wereprecipitated in a 0.43% aqueous gelatin solution in a ratio of gelatinto silver halide of 1:14. The emulsion was ripened at 49 C. for 15minutes and then ammonium hydroxide (50 ml. of 20% NH solution) wasadded and ripening continued for 30 seconds longer. There was then added50 ml. of a 5% aqueous solution of sodium dodecyl sulfate. Ripening wascontinued for 2 minutes and then acetic acid was added to lower the pHto 5. The emulsion was cooled to 18 C. and the resulting coagulum wasallowed to settle. The supernatant liquid was carefully decanted fromthe coagulated curds. The curds were washed with 5 liters of anacidified 2% solution of sodium chloride. One liter of distilled waterwas added to the curds and the mixture was stirred for 5 minutes. Atthis time 2l0 grams of deionized high molec ular weight polyvinylalcohol (PVA) was added in the form of a 3.5% aqueous solution. Enoughdilute sodium hydroxide solution was added to raise the pH to 7.5 andthe coagulum was redispersed by stirring for 5 minutes. The temperaturewas raised to 60 C. during which gold and sulfur sensitizers were added.The resulting emulsion was digested for 40 minutes. The digestedemulsion was cooled to about 43 C., final additions as set forth inExample I were added, and the pH was adjusted to with diisopropylamine.The final emulsion ready for coating was completely homogeneousindicating complete compatibility of the gelatin complex with polyvinylalcohol. The film was coated on the film support referred to in ExampleI in a manner to give a coating weight of 72 mg. AgBr/dm The film wasdried in the conventional manner. The film and an all-gelatin cinepositive emulsion film as a control were exposed and processed in themanner described in Example I and gave the following sensitometricresults.

Emulsion Relative Gamma Fog Speed Control s. 100 2. 39 .02 PVA emulsion87 2. 35 .02

The polyvinyl alcohol emulsion showed very high resist'ance todimensional change, blistering and deterioration under the influence ofhigh intensity are light projection.

Example III Example II was repeated in every detail except the finalemulsion was coated to give a coating weight of mg/dm. This may beaccomplished by either viscosity change, coating speed change or both,all of which are well known to those skilled in the art. The coatedelement was exposed and processed as described in Example I and thesensitometric results were as follows:

Emulsion Relative Gamma Fog Speed All gelatin control 100 2. 37 O1 PVAemulsion 132 2. 24 .05

The polyvinyl alcohol (PVA) emulsion had very high resistance toblistering and deterioration under the influence of high intensity arelight projection.

Example 1V Emulsion Relative Gamma Fog S peed Both polyvinyl alcoholemulsions showed good resistance to dimensional change, blistering anddeterioration under the influence of high intensity are lightprojection.

Example V A silver iodobromide emulsion was made in the man nerdescribed in Example I containing approximately grams of silver halidesand 10 grams of gelatin. The silver halides constituted about 96.4 molpercent bromide and 3.6 mol percent iodide. To this emulsion, whichamounted to about 740 grams including the water, there was added 100 ml.of distilled water containing 10 ml. of glacial acetic acid and 12 ml.of a 9% solution of a water-soluble, acid-soluble partial acetal. ofpolyvinyl alcohol and the sodium salt of o-sulfobenzaldehyde consistingof 5 grams of sulfonate sulfur per 100 grams of polymer. The temperaturewas adjusted to about 15 C. and 65 ml. of 3 N H 50 was added to lowerthe pH to 2.8-3.0. The resulting coagulum was allowed to settle in themanner described in Moede U.S. Patent 2,772,165. After removing thesupernatant liquid by decantation the curds were washed twice with 8liters of distilled water to remove the soluble Salts. Five hundredgrams of the Washed curds were redispersed in 2400 ml. of distilledwater containing 30 grams of gelatin by adjusting the pH 3 N potassiumchloride solution. Gold and sulfur sensitizers in excess were then addedand the emulsion was digested for 30 minutes at 63 C. The emulsion wascooled to 27 C. and the pn was lowered to 4.5 with 25 ml. of acetic acidsolution which brought about the coagulation of the suspended matter.After decanting the supernatant liquid the resulting coagulum was washedonce with distilled water to remove excess sensitizers. To the curdsfree of supernatant liquid there was added 400 ml. of a 5% aqueoussolution of sodium dodecyl sulfate. The pH was adjusted to 6.3 withaqueous sodium hydroxide and the curds were redispersed by stirring for5 minutes at about 38 C. The total weight of the emulsion was adjustedto 1090 grams With water. T hree-hundred gram portions of this emulsionwere each mixed with (I) 450 grams of a aqueous gelatin solution and (H)450 grams of a 15% aqueous solution of deionized high molecular weightpolyvinyl alcohol. The emulsions after thorough mixing were coated on.polyester film supports, dried at room temperature and exposed andtested as described in Example -I. The results are shown in thefollowing table.

The polyvinyl alcohol emulsion showed much higher resistance todimensional change, blistering and deterioration under high intensityare light projection.

The deionization of the polyvinyl alcohols of the foregoing examples wasmade by passing the PVA through a mixed bed ion exchange column.

Any silver halide emulsion may be made by the process. For example,silver bromochloride emulsions for use in graphic arts films may be madein the manner described above and are of value because of theirdimensional stability. The emulsions of the invention are also useful inthe manufacture of radiographic films.

The process of the invention is also useful in making emulsions whichare optically sensitized with cyanine, carbocyanine and merocyanine dyesof the usual types which are known to be optical sensitizers for gelatinphotographic emulsions. The process of the invention may also be used inpreparing color photographic emulsions in multilayer structures whereincolor couplers or color formers, bleach-out dyes and other dyes anddyeformers are incorporated in the emulsion layers. The emulsions may becoated on any suitable support such as paper, hydrophobic organicpolymer film supports including those disclosed in Alles et al., US.2,627,088, and cellulose ester supports, e.g. cellulose acetate films.They may also be coated on glass, metal, cardboard, etc. Specialanchoring layers may be necessary for some supports but these arewell-known to technicians skilled in the manufacture of photographicmaterials.

As indicated above, there are a large number of anion soaps which areuseful in the invention. The classification of these compounds isdiscussed in the book Kolloidchernische Grundlagen der Textilveredlungby Dr. E. Valko, 1937, at pages 5l9522, to which reference is made forthe meaning of the expression anion soaps. Generally the class alsoincludes soluble salts of longchain alkyl carboxylic acids, e.g. solublesalts of fatty acids containing eight or more carbons as, for example,lauric, oleic, ricinoleic, linoleic, stearic and palmitic. Thesecompounds, however, are much less satisfactory than long chain alkylsulfates and sulfonates. Soluble salts of long-chain alkyl sulfonicacids, soluble salts of sulfated higher fatty alcohols in which thealkyl group contains at least 8 carbons and many other sulfonated andsulfated aliphatic and aromatic compounds which are 0) water soluble andcontain from 10 to 20 carbon atoms are suitable complexing agents. 7

The invention provides a method of making emulsions wherein theprincipal colloid carrier is a vinyl alcohol polymer, e.g. polyvinylalcohol. Such emulsions have outstanding advantages over gelatin silverhalide er'n'ul sions and have resistance to deterioration by inicro=organisms. They are very dimensionally stable and have high resistanceto deterioration under conditions of ex posure to the intense heat ofhigh intensity are light pro jectors. The processes of the inventionalso oifer a con venient means of varying the silver halide to hinderratio which is quite important in certain photographic ele-- mentsrequiring a high concentration of silver.

The emulsions of the invention are also adapted to be made in hi hlyconcentrated form and even in sub-' stantially dry form for shipment anduse at a later time by adding a sufficient amount of water for coatingby any of the techniques known in the art, i.e. skim coating, extrusioncoating and spray coating. One important ad vantage of the processes ofthe invention is that gelatincomplexes can be made which arewater-soluble, and compatible with water-soluble polyvinyl alcohols0lutions and do not require organic solvents in the system. Still otheradvantages will be apparent from the forego ing description andfollowing claims.

We claim:

1. A method of preparing a photographic emulsion which comprisesdispersing silver halide in an aqueous gelatin solution, adding theretoan anion soap thereby forming a gelatin-anion soap complex containingdispersed silver halide grains and dispersing said complex in a watersoluble polyvinyl alcohol binder in a predominantly aqueous solution,said polyvinyl alcohol binder prepared by hydrolyzing a polyvinyl esterto an extent of at least percent.

2. A method of preparing a photographic emulsion which comprisesdispersing silver halide in an aqueous gelatin solution, adding theretoan anion soap thereby forming a gelatin-anion soap complex containingdispersed silver halide grains, coagulating the said complex thus formedand redispersing the said complex in a water soluble polyvinyl alcoholbinder in a predominantly aqueous solution, said polyvinyl alcoholbinder prepared by hydrolyzing a polyvinyl ester to an extent of atleast 80 percent.

3. A method of preparing a photographic emulsion which comprisesdispersing silver halide in an aqueous gelatin solution, adding an anionsoap thereby forming a gelatin-anion soap complex containing dispersedsilver halide grains, coagulating the said complex thus formed byadjusting the pH of the emulsion to less than 7, separating thecoagulated complex, redispersing the said complex in a water solublepolyvinyl alcohol binder in a predominantly aqueous solution, saidpolyvinyl alcohol binder prepared by hydrolyzing a polyvinyl ester to anextent of at least 80 percent and concurrently readjusting the pH toabout 7.

4. Method according to claim 3 wherein the anion soap is sodium dodecylsulfate.

5. Method according to claim 3 wherein the aqueous gelatin solutioncontains from 7 to 20 grams of gelatin per mole of silver halide.

6. Method according to claim 3 wherein the aqueous polyvinyl alcoholbinder solution contains from 70 to 200 grams of polyvinyl alcohol and'7 to 20 grams of gelatin per mole of silver halide.

7. A method of preparing a photographic emulsion which comprisesdispersing silver halide in an aqueous gelatin solution, coagulatingsaid dispersion by the addition of a water soluble, acid soluble partialacetal of polyvinyl alcohol and the sodium salt of o-sulfobenzaldehyde,adjusting the pH to below 4.5, redispersing the coagulum by readjustingthe pH to above 6, adding thereto an anion soap thereby forming agelatin-anion soap 9 complex containing dispersed silver halide grainsand dispersing said complex in a Water soluble polyvinyl alcohol binderin a predominantly aqueous solution, said polyvinyl alcohol binderprepared by hydrolyzing a polyvinyl ester to an extent of at least 80percent.

8. A photographic emulsion comprising silver halide dispersed in agelatin-anion soap complex, said complex being dispersed in a polyvinylalcohol binder in a predominantly aqueous solution, said polyvinylalcohol binder prepared by hydrolyzing a polyvinyl ester to an extent ofat least 80 percent.

9. An emulsion as described in claim 8 wherein the anion soap is sodiumdodecyl sulfate.

10. An emulsion as described in claim 8 wherein the 10 gelatin ispresent in an amount from 7 to 20 grams per mole of silver halidepresent.

11. An emulsion as described in claim 3 wherein the polyvinyl alcohol ispresent in an amount from 70 to 200 grams and said gelatin in an amountfrom '7 to 20 grams per mole of silver halide present.

References Cited in the file of this patent UNITED STATES PATENTS 102,489,341 Waller et al. Nov. 29, 1949 2,527,261 Hart et al. Oct. 24,1950 2,614,930 Lowe et al Oct. 21, 1952 2, 52,246 Weaver June 26, 1956

1. A METHOD OF PREPARING A PHOTOGRAPHIC EMULSION WHICH COMPRISESDISPERSING SILVER HALIDE IN AN AQUEOUS GELATIN SOLUTION, ADDING THERETOAN ANION SOAP THEREBY FORMING A GELATIN-ANION SOAP COMPLEX CONTAININGDISPERSED SILVER HALIDE GRAINS AND DISPERSING SAID COMPLEX IN A WATERSOLUBLE POLYVINYL ALCOHOL BINDER IN A PREDOMINANTLY AQUEOUS SOLUTION,SAID POLYVINYL ALCOHOL BINDER PREPARED BY HYDROLYZING A POLYVINYL ESTERTO AN EXTENT OF AT LEAST 80PERCENT.